A converter, such as a rectifier or a combined rectifier/inverter, may have a capacitance connected between its DC (Direct Current) poles. One example of the rectifier is a diode bridge which obtains its supply from an AC (Alternating Current) source, which is a 50 or 60-Hz AC network, for instance. Such a rectifier may then feed for example, one or more inverters or other loads via a DC link.
The capacitance connected between the DC poles of the rectifier may need to be charged before the rectifier is connected to the AC network in order to avoid a current surge upon the connection. Such a current surge may trigger protection of the system or disturb feeding AC network, for example. The capacitance connected between the DC poles of the rectifier may be charged to or close to a normal operating value of the capacitance. Such a normal operating value of the capacitance may correspond to a full-wave rectified voltage of the AC network, for example.
Such a charging of the capacitance connected between the DC poles of the rectifier may be implemented by means of charging resistors by using one or more of the phases of the AC network. An issue related to the use of such charging resistors is that they need to be sized on a case-by-case basis. For example a cyclic use that requires frequent charging needs to be taken into account. In addition, such charging resistors may cause considerable losses during the charging.
Another possibility for charging of the capacitance connected between the DC poles of the rectifier is to implement the charging by using semiconductors. An issue with utilizing semiconductors is that the solution may become complex and expensive because the semiconductors need to be sized according to possibly high instantaneous charging current values.